1. Field
The embodiments herein are directed to a radio resource allocation release system and roadside equipment and in-vehicle equipment that can communicate with another in-vehicle.
2. Description of the Related Art
Conventionally, an ITS (Intelligent Transport Systems), integrating a road and a vehicle, has been known to attempt to improve safety, transportation efficiency and comfort. For example, conventionally, a system attempts to achieve these improvements by road-vehicle communication performed between a base station (roadside equipment) placed on the road and a mobile station (in-vehicle equipment) mounted on the vehicle and by vehicle-vehicle communication performed between the mobile stations.
For example, conventionally in road-vehicle communication by spot communication for limiting a communication area as a road-vehicle area, in a synchronous time-division communication full-duplex communication uses different frequencies for communication from the base station to the mobile station and for communication from the mobile station to the base station, and a communication frame is time-divided into fixed-length sections called slots. The communication is performed between a single base station and a plurality of mobile stations.
To perform the communication by using the synchronous time-division communication system, the base station (roadside equipment) needs to allocate the slot as the radio resource to the mobile station (in-vehicle equipment). For example, conventionally, a method for allocating the radio resource to the in-vehicle equipment by the roadside equipment, the roadside equipment inquires each in-vehicle equipment of necessity of the radio resource, and then each in-vehicle equipment notifies the roadside equipment of this response.
In the above described technique for allocating the radio resource to each in-vehicle equipment, the roadside equipment allocates the radio resource to each in-vehicle equipment that responds to inquiry for necessity of the radio resource no matter whether or not the in-vehicle equipment exists in the road-vehicle area covered by the roadside equipment. However, the radio resource may be allocated to the in-vehicle equipment that exists outside of the road-vehicle area according to a request of the in-vehicle equipment, so that the radio resource may be depleted. Therefore, problems may occur in that the radio resource may not be allocated to the in-vehicle equipment that newly enters an area, and the in-vehicle equipment is therefore unable to perform communication in the area.